The working of a Hall-effect electric thruster and the role of its various constituent elements, namely an anode, a cathode, a magnetic circuit, and a heater of the cathode, are properly known to the person skilled in the art. An example that may be cited is “Fundamentals of Electric Propulsion: Ion and Hall Thrusters”, Dan M. Goebel and Ira Katz, JPL Space Science and Technology Series, March 2008. They are only briefly recalled here.
In a steady state, plasma forms at the anode and the cathode and the propulsion comes from the electrostatic acceleration generated by the positive ions. A propellant gas, usually xenon, is injected into the anode and collides with the electrons held there by a magnetic field and thereby renewing the plasma.
A conventional Hall-effect electric thruster is powered by an electric power supply system commonly referred to as the Power Processing Unit (PPU).
FIG. 1 illustrates a standard electric power supply system 1 of a Hall-effect electric thruster.
This electric power supply system typically consists of separate power supply sources to drive the different elements of the Hall-effect electric thruster.
In FIG. 1, the voltage sources are indicated by the symbol ± and the current intensity sources by the symbol ↑.
The electric power supply system 1 includes:                a first power supply source 10 for supplying power to anode 50,        a second power supply source 11 for supplying power to the heater 53 to heat the cathode 51, and to enable it to emit electrons, and        a power supply unit 12 for supplying power to a component close to the emitting part of the cathode, called the igniter 52.        
The first power supply source 10 is a direct, high-voltage source, and provides the major portion of the electric power required for the functioning of the Hall-effect electric thruster.
The second power supply source 11 is a current source.
The power supply unit 12 consists of a first unit, called the ignition module 121, combined and switchable with a second unit, called the support module 122. Generally speaking, the ignition module 121 includes a voltage square pulse generator, or a high voltage direct source, and the support module 122 includes a current source.
The first 10 and second 11 power supply sources and the power supply unit 12 are all together connected to the cathode 51 which is the voltage reference, usually known as the CRP (Cathode Reference Point).
A complex ignition process needs to be initialised to attain the steady state. \
The cathode 51 is preheated, usually for a few minutes, by the heater 53. Simultaneous to this heating phase, or following the same, voltage is applied between the igniter 52 and the cathode 51. A very weak electric current is established between the cathode 51 and the igniter 52 facilitated by the thermionic effect due to the heating of the cathode 51 by the heater 53. The voltage is applied until plasma is generated in cathode 51. For certain cathode technologies, high direct voltage in the range of 100 to 500 V is adequate. For other technologies, voltage is applied in the form of rectangular pulses, between 0 and 100-500 V, each, typically, lasting a few milliseconds at a frequency of ˜10 Hz, which increases the reliability of the ignition during the entire service life of the Hall-effect electric thruster. Voltage in the form of rectangular pulses may possibly be combined with a direct voltage ranging between 50 and 150 V.
When the plasma is generated at the level of cathode 51, the electrical conductivity between the latter and the igniter 52 is significantly increased such that the intensity of the current circulating in the igniter 52 increases.
An electronic control sensor detects this increase in current and then cuts off the ignition module 121. It may also be contemplated that the electronic control sensor automatically cuts off the ignition module 121 after a predefined time period.
During a subsequent phase, called the support phase, the electronic control sensor applies a weaker voltage to the igniter 52, via the support module 122, in a pulsed or continuous form.
This support phase typically lasts until a discharge current appears between the anode 50 and the cathode 51 and creates plasma in anode 50. The Hall-effect electric thruster is then switched on.
The management of the power supply of the igniter 52 proves to be very complex (multiple sources of power, electronic control sensor, switching from one mode of operation to the other), which contributes to increase in the cost, volume and mass of the Hall-effect electric thruster and its power processing units (PPU). In addition, the number and complexity of electronic devices affect the reliability of said Hall-effect electric thruster, which necessitates over-sizing and/or redundancies, thus raising the cost, volume and mass even more. In this regard, the PPU proves to be the most critical part of the electric propulsion.
U.S. Pat. No. 8,024,917, for example, proposes simplifying the PPU, at the level of the electric supply unit of the igniter, by using a multipurpose and common supply source, providing power supply to the heater, igniter, anode and possibly the control magnetic circuit of the plasma. A switch is configured to turn off the power supply to the heater through a first electronic device. When the switch is in the closed position, the common power supply source powers the heater, and no current flows through the other two circuits powering the anode and the igniter. Then, when a predefined criterion, for example a time period, a voltage, an intensity of current or a temperature, is verified, the first electronic device causes the switch to flip to the open position, which thereby cuts off the power supply to the heater. The voltage across the terminals of the igniter and the anode is thus equal to the voltage of the open circuit of the power supply, typically 300 V. The voltage is sufficient to cause a discharge current to appear in the space between the cathode and the igniter. The voltage between the cathode and the igniter then drops below the voltage at the terminals of the anode. A flow of electrons is created and flows from the cathode towards the anode, which is at a higher voltage, such that a discharge current is established between the cathode and the anode creating plasma. The electric thruster is thus switched on. The opening of a second switch enables a second electronic device to cut off the power supply to the igniter.
However, the power supply of the igniter remains very complex.
One can also cite U.S. Pat. No. 6,304,040 that describes an electric power supply system of a Hall-effect electric thruster. A voltage at the terminals of the igniter and the anode is generated in the form of pulses by means of a switch controlled by logic control, until the appearance of a discharge current in the space between the cathode and the igniter. The power supply system also proves to be complex and costly, particularly due to the use of an inductance.